The DNR is closing the trails because they were built without permits and the agency cannot ensure public safety. DNR said the bridges and structures were built without engineering design. There are no formal agreements about maintenance, and there is no liability coverage.
The DNR was concerned about erosion but the mountain bikers building the trails built bridges over all creeks and places where erosion might occur.
In Capitol Forest, the DNR has already taken some trails out and is looking at others. Maybe DNR could issue permits to mountain biking organizations that want to build trails on DNR land.